Molecular and cellular neurosciences [journal]
- MCP-1 mediated activation of microglia promotes white matter lesions and cognitive deficits by chronic cerebral hypoperfusion in mice. [JOURNAL ARTICLE]
- Mol Cell Neurosci 2016 Aug 12.
Microglia activation played a vital role in the pathogenesis of white matter lesions (WMLs) by chronic cerebral hypoperfusion. In addition, hypoxia induced up-regulated expression of MCP-1, promotes the activation of microglia. However, the role of MCP-1 mediated microglia activation in chronic cerebral ischemia is still unknown. To explore that, chronic cerebral hypoperfusion model was established by permanent stenosis of bilateral common carotid artery in mice. The activation of microglia and the related signal pathway p38MAPK/PKC in white matter, and working memory of mice were observed. We found that stenosis of common carotid arteries could induce MCP-1 mediated activation of microglia through p38MAPK/PKC pathway and white matter lesions. Taken together, our findings represent a novel mechanism of MCP-1 involved in activation of microglia, and provide a novel therapeutical strategy for chronic cerebral hypoperfusion.
- Early-life seizures alter synaptic calcium-permeable AMPA receptor function and plasticity. [JOURNAL ARTICLE]
- Mol Cell Neurosci 2016 Aug 10.
Calcium (Ca(2+))-mediated(4) signaling pathways are critical to synaptic plasticity. In adults, the NMDA glutamate receptor (NMDAR) represents a major route for activity-dependent synaptic Ca(2+) entry. However, during neonatal development, when synaptic plasticity is high, many AMPA glutamate receptors (AMPARs) are also permeable to Ca(2+) (CP-AMPAR) due to low GluA2 subunit expression, providing an additional route for activity- and glutamate-dependent Ca(2+) influx and subsequent signaling. Therefore, altered hippocampal Ca(2+) signaling may represent an age-specific pathogenic mechanism. We thus aimed to assess Ca(2+) responses 48h after hypoxia-induced neonatal seizures (HS) in postnatal day (P)10 rats, a post-seizure time point at which we previously reported LTP attenuation. We found that Ca(2+) responses were higher in brain slices from post-HS rats than in controls and this increase was CP-AMPAR-dependent. To determine whether synaptic CP-AMPAR expression was also altered post-HS, we assessed the expression of GluA2 at hippocampal synapses and the expression of long-term depression (LTD), which has been linked to the presence of synaptic GluA2. Here we report a decrease 48h after HS in synaptic GluA2 expression at synapses and LTD in hippocampal CA1. Given the potentially critical role of AMPAR trafficking in disease progression, we aimed to establish whether post-seizure in vivo AMPAR antagonist treatment prevented the enhanced Ca(2+) responses, changes in GluA2 synaptic expression, and diminished LTD. We found that NBQX treatment prevents all three of these post-seizure consequences, further supporting a critical role for AMPARs as an age-specific therapeutic target.
- Thyroid hormones are essential to preserve non-proliferative cells of adult neurogenesis of the dentate gyrus. [JOURNAL ARTICLE]
- Mol Cell Neurosci 2016 Aug 5.:1-10.
Thyroid hormones (THs) regulate adult hippocampal neurogenesis, a process that involves both cell populations that dynamically switch between pools of proliferative and quiescent cells, and cells that definitely leave the cell cycle to maturate into granular neurons. This investigation was carried out to determine the role of THs on the mitotic activity of specific proliferative cell populations and the preservation of non-proliferative cells participating in the neurogenic process of the dentate gyrus (DG) of the hippocampus. Hypothyroidism was induced in male adult Wistar rats with methimazole for 28days. We quantified the total number of proliferative cells (BrdU+), proliferative type 1 (BrdU+/GFAP+), and 2b and 3 (BrdU+/DCX+) cells. Early non-proliferative cells (BrdU-/DCX+ cells lacking dendritic process), postmitotic neuroblasts (Tuj 1+ cells lacking dendritic process), and immature granular neurons (IGN; DCX+ or Tuj 1+ and the presence of dendritic processes into granular or molecular layer) were also included. The evidence showed that the proliferation of Type 1, 2b and 3 cells is not modified by hypothyroidism. In contrast, hypothyroidism reduced the number of early non-proliferative cells and also leads to a decrement in the number of IGN. Our results show that proliferative cells of the DG are not sensitive to thyroid perturbations. However, THs are essential to preserve cell populations that leave the cell cycle in the DG of the hippocampus.
- Exploration of physical and chemical cues on retinal cell fate. [JOURNAL ARTICLE]
- Mol Cell Neurosci 2016 Aug 4.:122-132.
Identification of the key components in the physical and chemical milieu directing donor cells into a desired phenotype is a requirement in the investigation of bioscaffolds for the advancement of cell-based therapies for retinal neurodegeneration. We explore the effect of electrospun poly-ε-caprolactone (PCL) fiber scaffold topography and functionalization and culture medium, on the behavior of mouse retinal cells. Dissociated mouse retinal post-natal cells were seeded on random or aligned oriented fibers, with or without laminin coating and cultured with either basic or neurotrophins enriched medium for 7days. Addition of laminin in combination with neurotrophins clearly promoted cell- morphology, fate, and neurite extension. Nanotopography per se significantly affected cell morphology, with mainly bipolar profiles on aligned fibers and more multipolar profiles on random fibers. Laminin induced a remarkable 90° switch of neurite orientation. Herewith, we demonstrate that the chemical cue is stronger than the physical cue for the orientation of retinal neurites and describe the requirement of both neurotrophins and extracellular matrix proteins for extended neurite outgrowth and formation of complex retinal neuronal networks. Therefore, tailor-made PCL fiber mats, which can be physically and chemically modified, indeed influence cell behavior and hence motivate further retinal restorative studies using this system.
- Noise-induced hearing loss: Neuropathic pain via Ntrk1 signaling. [JOURNAL ARTICLE]
- Mol Cell Neurosci 2016 Jul 26.:101-112.
Severe noise-induced damage to the inner ear leads to auditory nerve fiber degeneration thereby reducing the neural input to the cochlear nucleus (CN). Paradoxically, this leads to a significant increase in spontaneous activity in the CN which has been linked to tinnitus, hyperacusis and ear pain. The biological mechanisms that lead to an increased spontaneous activity are largely unknown, but could arise from changes in glutamatergic or GABAergic neurotransmission or neuroinflammation. To test this hypothesis, we unilaterally exposed rats for 2h to a 126dB SPL narrow band noise centered at 12kHz. Hearing loss measured by auditory brainstem responses exceeded 55dB from 6 to 32kHz. The mRNA from the exposed CN was harvested at 14 or 28days post-exposure and qRT-PCR analysis was performed on 168 genes involved in neural inflammation, neuropathic pain and glutamatergic or GABAergic neurotransmission. Expression levels of mRNA of Slc17a6 and Gabrg3, involved in excitation and inhibition respectively, were significantly increased at 28days post-exposure, suggesting a possible role in the CN spontaneous hyperactivity associated with tinnitus and hyperacusis. In the pain and inflammatory array, noise exposure upregulated mRNA expression levels of four pain/inflammatory genes, Tlr2, Oprd1, Kcnq3 and Ntrk1 and decreased mRNA expression levels of two more genes, Ccl12 and Il1β. Pain/inflammatory gene expression changes via Ntrk1 signaling may induce sterile inflammation, neuropathic pain, microglial activation and migration of nerve fibers from the trigeminal, cuneate and vestibular nuclei into the CN. These changes could contribute to somatic tinnitus, hyperacusis and otalgia.
- The absence of pleiotrophin modulates gene expression in the hippocampus in vivo and in cerebellar granule cells in vitro. [JOURNAL ARTICLE]
- Mol Cell Neurosci 2016 Jul 26.:113-121.
Pleiotrophin (PTN) is a secreted growth factor recently proposed to act as a neuromodulatory peptide in the Central Nervous System. PTN appears to be involved in neurodegenerative diseases and neural disorders, and it has also been implicated in learning and memory. Specifically, PTN-deficient mice exhibit a lower threshold for LTP induction in the hippocampus, which is attenuated in mice overexpressing PTN. However, there is little information about the signaling systems recruited by PTN to modulate neural activity. To address this issue, the gene expression profile in hippocampus of mice lacking PTN was analyzed using microarrays of 22,000 genes. In addition, we corroborated the effect of the absence of PTN on the expression of these genes by silencing this growth factor in primary neuronal cultures in vitro. The microarray analysis identified 102 genes that are differentially expressed (z-score>3.0) in PTN null mice, and the expression of eight of those modified in the hippocampus of KO mice was also modified in vitro after silencing PTN in cultured neurons with siRNAs. The data obtained indicate that the absence of PTN affects AKT pathway response and modulates the expression of genes related with neuroprotection (Mgst3 and Estrogen receptor 1, Ers 1) and cell differentiation (Caspase 6, Nestin, and Odz4), both in vivo and in vitro.
- Calpain-dependent truncated form of TrkB-FL increases in neurodegenerative processes. [JOURNAL ARTICLE]
- Mol Cell Neurosci 2016 Jul 20.:81-92.
Recent findings indicate that the mechanisms that drive reshaping of the nervous system are aberrantly activated in epilepsy and several neurodegenerative diseases. The recurrent seizures in epilepsy, particularly in the condition called status epilepticus, can cause permanent neurological damage, resulting in cognitive dysfunction and other serious neurological conditions. In this study, we used an in vitro model of status epilepticus to examine the role of calpain in the degeneration of hippocampal neurons. We grew neurons on a culture system that allowed studying the dendritic and axonal domains separately from the cell bodies. We found that a recently characterized calpain substrate, the neurotrophin receptor TrkB, is cleaved in the dendritic and axonal domain of neurons committed to die, and this constitutes an early step in the neuronal degeneration process. While the full-length TrkB (TrkB-FL) levels decreased, the truncated form of TrkB (Tc TrkB-FL) concurrently increased, leading to a TrkB-FL/Tc TrkB-FL imbalance, which is thought to be causally linked to neurodegeneration. We further show that the treatment with N-acetyl-Leu-Leu-norleucinal, a specific calpain activity blocker, fully protects the neuronal processes from degeneration, prevents the TrkB-FL/Tc TrkB-FL imbalance, and provides full neuroprotection. Moreover, the use of the TrkB antagonist ANA 12 at the time when the levels of TrkB-FL were significantly decreased, totally blocked neuronal death, suggesting that Tc TrkB-FL may have a role in neuronal death. These results indicate that the imbalance of these neurotrophins receptors plays a key role in neurite degeneration induced by seizures.
- Orexin A attenuates palmitic acid-induced hypothalamic cell death. [JOURNAL ARTICLE]
- Mol Cell Neurosci 2016 Jul 21.:93-100.
Palmitic acid (PA), an abundant dietary saturated fatty acid, contributes to obesity and hypothalamic dysregulation in part through increase in oxidative stress, insulin resistance, and neuroinflammation. Increased production of reactive oxygen species (ROS) as a result of PA exposure contributes to the onset of neuronal apoptosis. Additionally, high fat diets lead to changes in hypothalamic gene expression profiles including suppression of the anti-apoptotic protein B cell lymphoma 2 (Bcl-2) and upregulation of the pro-apoptotic protein B cell lymphoma 2 associated X protein (Bax). Orexin A (OXA), a hypothalamic peptide important in obesity resistance, also contributes to neuroprotection. Prior studies have demonstrated that OXA attenuates oxidative stress induced cell death. We hypothesized that OXA would be neuroprotective against PA induced cell death. To test this, we treated an immortalized hypothalamic cell line (designated mHypoA-1/2) with OXA and PA. We demonstrate that OXA attenuates PA-induced hypothalamic cell death via reduced caspase-3/7 apoptosis, stabilization of Bcl-2 gene expression, and reduced Bax/Bcl-2 gene expression ratio. We also found that OXA inhibits ROS production after PA exposure. Finally, we show that PA exposure in mHypoA-1/2 cells significantly reduces basal respiration, maximum respiration, ATP production, and reserve capacity. However, OXA treatment reverses PA-induced changes in intracellular metabolism, increasing basal respiration, maximum respiration, ATP production, and reserve capacity. Collectively, these results support that OXA protects against PA-induced hypothalamic dysregulation, and may represent one mechanism through which OXA can ameliorate effects of obesogenic diet on brain health.
- Phenotypic screening with primary neurons to identify drug targets for regeneration and degeneration. [JOURNAL ARTICLE]
- Mol Cell Neurosci 2016 Jul 18.
High-throughput, target-based screening techniques have been utilized extensively for drug discovery in the past several decades.However, the need for more predictive in vitro models of in vivo disease states has generated a shift in strategy towards phenotype-based screens.Phenotype based screens are particularly valuable in studying complex conditions such as CNS injury and degenerative disease, as many factors can contribute to a specific cellular response.In this review, we will discuss different screening frameworks and their relative utility in examining mechanisms of neurodegeneration and axon regrowth, particularly in cell-based in vitro disease models.
- Anti-amyloidogenic effects of glycosphingolipid synthesis inhibitors occur independently of ganglioside alterations. [JOURNAL ARTICLE]
- Mol Cell Neurosci 2016 Jul 1.:63-70.
Evidence has suggested that ganglioside abnormalities may be linked to the proteolytic processing of amyloid precursor protein (APP) in Alzheimer's disease (AD) and that pharmacological inhibition of ganglioside synthesis may reduce amyloid β-peptide (Aβ) production. In this study, we assessed the usefulness of two well-established glycosphingolipid (GSL) synthesis inhibitors, the synthetic ceramide analog D-PDMP (1-phenyl 2-decanoylamino-3-morpholino-1-propanol) and the iminosugar N-butyldeoxynojirimycin (NB-DNJ or miglustat), as anti-amyloidogenic drugs in a human cellular model of AD. We found that both GSL inhibitors were able to markedly inhibit Aβ production, although affecting differently the APP cleavage. Surprisingly, the L-enantiomer of PDMP, which promotes ganglioside accumulation, acted similarly to D-PDMP to inhibit Aβ production. Concurrently, both D- and L-PDMP strongly and equally reduced the levels of long-chain ceramides. Altogether, our data suggested that the anti-amyloidogenic effects of PDMP agents are independent of the altered cellular ganglioside composition, but may result, at least in part, from their ability to reduce ceramide levels. Moreover, our current study established for the first time that NB-DNJ, a drug already used as a therapeutic for Gaucher disease (a lysosomal storage disorder), was also able to reduce Aβ production in our cellular model. Therefore, our study provides novel information regarding the possibilities to target amyloidogenic processing of APP through modulation of sphingolipid metabolism and emphasizes the potential of the iminosugar NB-DNJ as a disease modifying therapy for AD.